(a) Technical Field
The present invention relates to a polylactic acid composition with improved heat-resistance and improved impact-resistance. More particularly, the present invention relates to a polylactic acid composition in which both impact strength and heat-resistance are improved by a mixture of polyketone with modified rubber.
(b) Background Art
Polylactic acid is a polymer made by synthesis of lactic acid as a monomer, in which the lactic acid is obtained by fermentation of starch, etc. extracted from corn, etc. as a renewable resource. When the polylactic acid is applied to interior/exterior parts of a vehicle, the heat resistance, impact resistance, and hydrolysis resistance of the polylactic acid must be improved.
Polyketone is a terpolymer obtained by polymerization of carbon monoxide, ethylene, and propylene as monomers, which requires cheaper raw materials and a polymerization process to make, when compared to general engineering plastic materials such as polyamide, polyester, and polycarbonate. Also, polyketone is known to have excellent heat resistance, chemical resistance, fuel permeation resistance, abrasion resistance, etc.
A conventional polymer material requiring petroleum resources as a raw material increases carbon dioxide concentration in the air when incinerated after its use. However, even though polylactic acid emits carbon dioxide through incineration or biodegradation, the emitted carbon dioxide originated from the air. Thus, the polylactic acid is a genuinely recyclable material which does not increase carbon dioxide concentration in the air since the carbon dioxide which is emitted originally came from the air.
Polylactic acid, however, is weak in impact resistance strength. Accordingly, in order to use the polylactic acid as structural materials such as car interior/exterior materials, research for overcoming its weakness through stiffeners such as natural fibers has been conducted (T. Inho and Y. Kageyama, SAE 2004-01-0730). In some automobile companies, a polylactic/natural fiber composite has been applied to parts such as a spare tire well cover. However, the composite has a disadvantage in that it is hydrolyzed by moisture absorption, resulting in a drop in its physical properties.
Also, in order to improve the heat resistance of polylactic acid, much research for blending the polylactic acid with polycarbonate, acrylonitrile butadiene styrene (ABS), polyethylene terephthalate (PET), polypropylene, etc. has been conducted. However, significant effects have not been obtained yet.